Abstract
Abstract. This work investigates the variability of ozone (O3), carbon monoxide (CO) and equivalent black carbon (BC) at the Italian Climate Observatory "O. Vittori" (ICO-OV), part of the Mt. Cimone global GAW-WMO station (Italy). For this purpose, ICO-OV observations carried out in the period January 2007–June 2009, have been analyzed and correlated with the outputs of the FLEXPART Lagrangian dispersion model to specifically evaluate the influence of biomass burning (BB) and anthropogenic emissions younger than 20 days. During the investigation period, the average O3, CO and BC at ICO-OV were 54 ± 3 ppb, 122 ± 7 ppb and 213 ± 34 ng m−3 (mean ± expanded uncertainty with p < 95%), with clear seasonal cycles characterized by summer maxima and winter minima for O3 and BC and spring maximum and summer minimum for CO. According to FLEXPART outputs, BB impact is maximized during the warm months from July to September but appeared to have a significant contribution to the observed tracers only during specific transport events. We characterised in detail five "representative" events with respect to transport scales (i.e. global, regional and local), source regions and O3, CO and BC variations. For these events, very large variability of enhancement ratios O3/CO (from −0.22 to 0.71) and BC/CO (from 2.69 to 29.83 ng m−3 ppb−1) were observed. CO contributions related with anthropogenic emissions (COant) contributed to 17.4% of the mean CO value observed at ICO-OV, with the warm months appearing particularly affected by transport events of air-masses rich in anthropogenic pollution. The proportion of tracer variability that is described by FLEXPART COant peaked to 37% (in May–September) for CO, 19% (in May–September) for O3 and 32% (in January–April) for BC. During May–September, the analysis of the correlation among CO, O3 and BC as a function of the COant indicated that ICO-OV was influenced by air-masses rich in anthropogenic pollution transported from the regional to the global scale. On the other side, CO and O3 were negatively correlated during October–December, when FLEXPART does not show significant presence of recent anthropogenic emissions and only a few observations are characterized by enhanced BC. Such behaviour may be attributed to an ensemble of processes concurrent in enhancing O3 with low CO (upper troposphere/lower stratosphere intrusions) and to O3 titration by NO in polluted air-masses along with lower photochemical activity. An intermediate situation occurs in January–April when CO and O3 were almost uncorrelated and BC enhancements were associated to relatively old (10 days) anthropogenic emissions.
Highlights
Tropospheric carbon monoxide (CO), ozone (O3) and black carbon (BC) have a substantial impact on climate and air quality
Over the 16 events detected by FLEXPART outputs, those having “local” biomass burning (BB) source were characterized for the greatest part (6/8 events) by clear CO enhancements ( CO > 0 ppb) in respect to the average behaviour obtained by applying the 21-day running mean, those having “global” sources were characterized by negative or non-significant CO (7/7) and the only event that was attributed to emission occurring at “regional” scale showed a positive CO
Cimone global GAW-WMO station (ICO-OV) and we investigated the influence of biomass burning (BB) and anthropogenic emissions younger than 20 days
Summary
Tropospheric carbon monoxide (CO), ozone (O3) and black carbon (BC) have a substantial impact on climate and air quality. Previous studies have shown that the atmospheric compounds directly emitted by BB or produced by photochemical processes occurring within BB plumes can be transported over long distances, affecting both air quality and climate from local to global scales A dryer and warmer climate in the Mediterranean region, as projected by climate models, can lead both to an increase in pollution sources such as wildfire events and to enhanced photochemical O3 production (Solomon et al, 2007) with a dramatic change in pollutant transport patterns over Europe (Forster et al, 2007). The Lagrangian atmospheric transport model FLEXPART provides an estimate of the emission age of BB and anthropogenic emissions at ICO-OV and, coupled to the observations, can allow to quantify the roles played by these emission types to the atmospheric composition variability
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